1. Field of the Invention
The present invention relates to a motor function analyzing apparatus that evaluates a motor function of a biological object using a magnetic sensor.
2. Description of the Related Art
Recently, the number of patients with movement disorder increases together with the progression of an aging society. Examples of such movement disorder are diseases that progress a disorder in motor function, such as Parkinson's disease, stroke, cervical myelopathy, dementia, and mental disorder. For example, Parkinson's disease that is a typical disease with movement disorder is an intractable disease which brings about a serious disorder in daily life because of tremor of hands, muscles rigidity, etc. The number of Parkinson's disease patients in Japan reaches 145,000 according to the survey by Japan Ministry of Health, Labor and Welfare in 2005, and it is expected that such number increases thereafter.
Conventionally, it is typical that a doctor checks and sees the motion of a patient and makes an evaluation based on scores representing severity levels in order to diagnose movement disorder. For example, in the case of a diagnosis to Parkinson's disease, a UPDRS (Unified Parkinson's Disease Rating Scale) is widely used as an evaluation index representing the severity level of Parkinson's disease. According to the UPDRS, a motor function is evaluated through plural motions, such as walking, and finger tapping motion (a motion of repeatedly opening/closing the thumb of a hand and the index finger thereof).
According to the UPDRS, however, evaluation is made through the subjective diagnosis by a doctor, so that there is an individual difference among doctors, resulting in insufficient objectivity in some cases. In order to overcome such a problem, apparatuses which measure the finger tapping motion by a patient using a magnetic sensor, and which evaluate a motor function quantitatively have been developed (see, for example, JP 2005-152053 A, JP 2008-246126 A and Kandori et al., “Quantitative magnetic detection of finger movements in patients with Parkinson's disease.”, Neuroscience Research. Vol. 49, No. 2, 2004, pp 253-260).
According to such apparatuses, magnetic sensors are attached to respective nail portions of a thumb and an index finger (hereinafter, referred to as “two fingers”), and a voltage value obtained from the magnetic sensors is converted into a distance value between the two fingers (corresponding to a distance between respective cushion sides of the thumb and the index finger). For example, a Non-patent Literature (Keisuke SHIMA, Eriko KAN, Toshio TSUJI, Tokuo TSUJI, Akihiko KANDORI, Tsuyoshi MIYASHITA, Masaru YOKOE, and Saburo SAKODA, “Magnetic sensor calibration for human finger tap measurement”, Society of Instrument and Control Engineers, Vol. 43, No. 9, 2007, pp 821-828) discloses a technology which measures three calibration points (e.g., data on three distances: 2 cm; 3 cm; and 6 cm) for the two fingers attached with magnetic sensors before measuring a finger tapping motion in order to obtain a correspondence between a voltage value and a distance value, and which substitutes such calibration points into a predetermined formula, thereby deriving a conversion formula of calculating a distance value from a voltage value.
According to the conventional technologies, however, when a calibration measurement includes an error, a calculated distance value may also include a large error in some cases. For example, when the two fingers are widely opened, even if the actual distance value between the two fingers is 15 cm, a value exceeding 30 cm may be falsely output in some cases. Also, according to the conventional technologies, it is necessary to perform three kinds of calibration measurement before a finger tapping motion is measured for every measurement, the management of instruments and the calibration measurement are bothersome.